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T. S. H.. who forwarded letter on "Readings from the Globes," is requested to send his address.

K. R> Scott (Rochdale) —For the sixpenny-piece you enclosed in your letter we had to pay Sd. The letter was not registered, and the Post Office authorities very correctly say tliey cannot undertake the transmission of coins: and in unregistered letters, as so sent, they are exposed to serious risk; but when registered they are practically safe. As a step towards the more general registration of all such letters, the fee has been reduced from fid. to Id., and it has been decided to register all letters unquestionably containing coin, even though they be posted, as in this case, without registration, and to charge them on delivery with a double fee of Sd., in addition to the ordinary postage.

J. R. T.—The ener arose from your indistinct writing. Be more particular in writing proper names.

G. Smith.—We don't know "J. C. H.'s" address. If vou have anything to say, and particularly ir you can speak

■» from experience, on the abuse of lunatic asylums, our columns are open to you.

Uruan next week.

To M Illiu.—In Mr. Sharpe's letter, p. 13+, for " saving of Hour" read " saving of power;" and for "20ft.," " 12ift" &c . read "20st," !«.

Iit. Swallpn—Ko stamps enclosed.

M.R.C.V..S.—Yes. Nodoubt many of our readers would like some information on "domestic pets."

Hknet W, Hinfkxy, next week. . E. Y -The library of the British Museum is free. Yntt must, however, get two householders to recommend you.

Tile Sixpenny 8ale Column is the only place in which can appear queries forwarded by O. C. C, S. U. (Pontefract), R. S. George (Sunderland).

T. Jones.—No, we cannot. There is no real remedy but the raior, and we suppose you will hardly care about tryiog that. Why waste our time and your own in writing about such nonsense?

A Constant Readxr.—You may do so without infringing anybody's " rights."

J. Mosedale.— June 4, 1869. In future consult index, and save us trouble of searching.

T. J. O'connor—Hardwirke, 192, Piccadilly, and Groombridge, Paternoster-row. The first is monthly, price Is. 6d., and the second quarterly, price 2s. 6d.

C. G— Cannot say. Wo do not estimate for publishing books. 6

R 8.—Yes.

W. B. B.—Apply to a medical man. The disease results from different causes, and it would be dangerous to advise.

John Beyce — Write them for a description.

J J. (Rotherham).—See back numbers.

W. Blao.—See page 114. present vol.

Fbatkr—Similar information has been given recently—more than once.

A Young Ttee.—Yours is only a different manifestation of the same disease. Let your friend apply to anv chemist. Third query inserted.

Cambridgeshire.—Your first two queries have been answered many times.

M. L, MorrATT.—The numbers in the indices refer to the pages.

Entomologist. — Your queries were answered at some ength in the early numbers of Vol. X.

James Bell—Your mention of the can of water experiment shows strong); how people wilfully misinterpret facta. The rest of your letter is simple assertion unsupported by argument.

Filius NtiLi.t is.— Can you not try it? The use of the sugai of lead was at the time strongly deprecated by one of the medical journals.

A. A. Toms.—All your queries have received answers in our pages many times.

Fan.—First ascertain whether electricity tan be applied in working the bells. It strikes us you are altogether in the dark.

Ciiahi.es T. W.—S7. Boulevard Bonnenouvelle, Paris.

II. Beveling—Thanks. The lines arc good, but not appropriate for "ours."

C. J. F.—If an illustration or description of your paten' appears in the Esolish Mechanic or any other paper you cannot patent it afterwards. Publishing it makes it public property.

Unequal Steam Pressure—We have received a Ions letter on this subject in answer to Mr. Ben Wood. Hail the letter been shorter and contained fewer personal reflections we should have inserted it. Why cannot correspondent*, in discussing scieutiticquestions, give each other credit for good intentions, and be more tolerant of each other's supposed shortcomings?

S. F. Shakespeare, of Thrapstone, writes ns to say that lit invented "the pedespeed " two years ago, and found it to answer very well. Is he sure it answered well? In what condition were his feet and ancles after using the invention a couple of hours?

W. R T— Answer through the English Mechanic. If such information is good for one it is good for a thousand.

J. B. R.— Cannot answer by post.

J. T. Mvjrpht— For information on Phantom Veloce see advertisement on second page.

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Ik obedience to tho suggestions of a number of readers, we hu.e decided on appropriating a portion or our space to a condensed iigt or patents |s nearly as possible up to the date of our issue.

APPLICATIONS FOR LETTERS PATENT PUKING THB WEEK ENDING APRIL 28, 1870.

1130 H. B. Barlow, Manchester, doors, locks aud latches.—A communication

1181 J. F. Spencer, Westminster, and V. Inglis, Bolton steam engines *

nsa 8. Barton, Manchester, distributing apparatus to be applied to garden hose.

H83 F.Taills, 88, Fleet-street, London, cocks for gas. orfor liquids or fluids,

1134 &, Cherry, Halifax, looms for weaving*.

1135 B. J. B. Mills, 36, Southampton-buridinss, studs, for buttons.—A communication

1130 S. C. Lister. Bradford, weaving silk and cotton velvet

1137 D. Forbes, York-place. Portraan-sijuare. and A. P. Price, 47. Lincolu's-ibn-tlcldji, improvements in the treatment of sewage

1138 E. Hoyle, Bradford, manipulating gold leaf for ornamenting

1130 M. Nolden, Franofort-on the-Mafne, curing or drying mealy and grainy stuffs, heating, cooling, and mixing fluid substances, and condensing gaseous ones

1140 D. Sowden and R. C. Stephenson, Bradford, boring. drilling, and turning wood or metal

1141 W Brown. Portsmouth, improvements in the construction of! hrust blocfci.plumraer blocks, and such like mechanism uvea in steam uliips

1143 H. W. HaminondSfMnnchester, manufacture of sunerphonphate ofllme.—A communication

1143 W R. Lake, Southampton-buildings, cartridges for breech-loading tlre-arras.—A communication ■ n"G-Us^mcN-(i;ud>nK-street.;Vauxhall.sndJ.W.iToung/Portland terrace. Regent'a-pnrk, portable apparatus for manufacturing gnu.

1145 A. V. Newton. 68, Chancery-lane, improved device for operating the throttle valve or regulator tn locomotive engines, and ibr.other like pnrposos.—A oommunleatiou • 1148 C. Cooke, Kensington, improved combination of articles used for culinary purposes.—A communication

nnii7 ll1i0.*J?.n.e,,'.B!?i[,,ft*.I,c'ir Newport, Monmouth, and G. W. Elliott, Chesterfield. Improvements in slide valvos

1148 B. B. (Sampson, Hope Mills, near Stroud, apparatus for feeding machinery employed in carding or preparing wool and other fibrous substances

1140J. .Green, Wrexham, manufacture of coke, and the apparatus connected therewith

MM) W. Smith. Heywood, looms for weaving

. W-- c?,t *ad c- s- cru- Ipswich, wheels for carriages

1152 W. R. Lake, Southampton-buildings, condensers for marinpstwtm (inline*.—A oommnniration

1153 K, Sinclair, Nloagow, apparatus to promote circulation In locomotive steam hollers.—A communication

1154 w. it. Lake. 8ouihampton>buiid.nn. London, Improvements iu reversible butt hinges.—A communication

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analoifous conatruetlons

1103 O. Fenwick. Gateshead-on-Tyne, ropes or cables to be used for telegraphic or other purposes

liCil'. D. Suiin;rlaiid. King William-street, London, travelling haics and portmanteaus

I1M K. L. Parker. Hirmlngbam, Improvements in buckles or fastenings for braces

HOA J. Lord. Crawshaw Booth, J.'Qresty, Manchester, and C. Cross, Pendleton, apparatus for separatist and sorting cotton

1106 S. Kandall. Lmsttale. aud J. Bandall, Stevenage, consOruction of harrows

1107 O. J. Firmln. 10 Lorn-road, North Brixton, self- regis taring water or liquid gauges

1108 L, Wray, itamsgate. apparatus for ("rushing ores

PATENTS 8BALED.

3081 C. A. Ofverberg, filters and filtering apparatus—A com

munl ration 9008 J. Look wood, couplings for railway engines, carriages,

and waggons
8090 w. Blackett Halnrh. circular saw benches
8)00 J. H. Gnerson and K. Philips, bronzing, colouring, and

Ulumiuntlng card*, and paper
3103 J. P. Uennoldson. st«am lubricators
8104 J, Bodge, apparatus for forging or shaping metals

3107 T. HriggB. materials used for packing

2110 W. A. Martin and K. Wylnm, fuet-feeding and smekeoonnuming apparatus Tor furnaces

3184 J. Jame-», bending aud Jointing metallic or other sheet* so as to form boxes

3178 A. H. Brandon, motive-power engines, and in the meana and mechanism for generatiug such power.—A communication

3108 M. Wilson, Improvements in sink traps
3225 H. D. Davis, machinery for working rudders

3201 P. Clark, manufacture ur pipes, bricks, tiles, and other articles from clay

8&d9 W. N. MacCartney, improved railway carriage for paseoiignrs.—A communication

5«3 F. W. Webb, improvements in locomotive and other steam eiiemtfs and boilers

183 .T. Dewar, treatment of certain substances for manure

M0 J. Dewar, treatment of certain substances for food and for manure

415 W". K. Lake, apparatus for drying sugar.—A communication

410 B. Looker.eonstruction of horticultural structures, casee or enclosed spaces

004 H. Hay ward, manufacture or yarns and fabrics containing horse-hair

010 J. Allmann, machinery for dressing or sifting ground wheat or other grain—A communication

3100 O. Simpson, manufacture of miniature or toy bricks for the use of children

Sill A. Howater. rolling or shaping metals

8116 T. Clark, improved implements adapted for constructing tube wells and rim lug hollow piles

8136 W. W. Gird wood, seli-lubrieating metallic elastic packing

3188 T. Taylor and J. VT. Daviee, apparatus for singeing horses

3147 B. H. Monckton, improvements in electricity and means of telegraphing

t\5i .1. c. Mewbnrn. improvements in apparatus for feeding boilers, and lor raising and forcing fluids generally.—A. communication

3171 P. Jensen, guns for bayonet drill.—A communication

8174 R. Spice, artitlciai stone. —A communication

3)04 B. Finch, dock gates and caissons

341.1 L. M uunt. apparatus fur " filling " match splints or other splints

8401 .T. H. Johnson, spring mattredses.-A communication

***?D. rrideaiix. purii'ying ana calcining gas and soap limes

r»* H Morris and M. D. Penney, treating shoddy and otuor ant mil waste to obtain aminoutu ana salts of ainmuula there from

284 W. Hay. making paper

254 It. Hayworih, B, Woodcook, and J. M'Cabe, looms for weaving

4M G Twigg .shearing and clipping apparatus

4*7 O. Bartholomew, apparatus to be used In getting coal

600 B. G. George, pioduing pictorial, ornamental, and otlier designs and device*

«S3 A. Poison, treating grain and in the mechanism employed therefor

Sty (English Jpcrftamc

AND

MIRROR OF SCIENCE AND ART. FRIDAY. MAY 13. 1870.

ANCIENT COINS.—I.
Br Henry W. Henfbey.

IT is impossible to estimate too highly the great Talue of ancient coins as illustrators of history. Their influence extends to the remotest ages, ai.d the remotest oountries, and they are undoubtedly the most. veracious and imperial! able of historical records. "I soon pereeived," siys Admiral Smyth, "the mischievous error of the too general opinion, that an acquaintance with ancient coina is more the province of the antiquary than of the acholar, that it was of little permanent advantage to the general reader, and that it was useless to him whose avocations in life admit of but brief intervals for literary researchea. My conviction, on the contrary, showed that without these infallible vouchers, independent of their intimate connexion with the fine aits, there cannot be a clear understanding of many customs, offices, and historical events; that an experimental acquaintance with medals is a higher advantage than the ignorant will admit it to be; and that no one can be disparaged by a pursuit which engaged the attention of and enrolled among ita votaries such men as Alfred, Cromwell, Napoleon, Seldcn, Wren, Canova, Camden, Evelyn, and Cbantrey. Looking backwards to antiquity is not at all going back to it ;but the process inculcates various and invaluable cautionary lessons."

We now purpose to give a few particulars of the most interesting coins in the several serio", commencing with the Greek, as being the most ancient. The earliest of these were struck in the island of .Egina in the seventh century B.C. They have a tortoise or turtle on one side, and square indented marks on the other. In shape they are thick and globulons, being struck out of a bullet-shaped piece of silver, in order to a«sist the high relief. The different denominations o{ the Grecian silver coina were the drachma or drachm, the eighth part of an ounce, worth about 9d.: the didrachm, or double drachm, worth Is. Gd. ;the tridrachm (very rare), or piece of three drachms, worth 2s. 3d. ; and the tetradrachm, or piece of four drachms, worth about 3s. of our money. There are many divisions of the drachma which it is not necessary to notice here in detail, but they consisted of the obolas and ita multiples and divisions. The coins cf the Lydians are next to thoae of ^Egina in antiquity, and to these succeed the gold and silver Uarics of the Persians.

These Darics, struck under Cyrii3 or his nearer successors, are the pieces mentioned under the name of drama in the Bible, 1 Chronicles, xxix. 7; Ezra, ii. G9, viii. 27 ; Nehemiah, vii. 70, 711 "2. They were current in Palestine in the period after the return from Babylon. The Dariea which now exist are thick pieces of pure gold, weighing about 128 grains troy ; and bear obrtrse, the figure of a King of Persia kneeling with a bow and javelin, or a bow und a dagger; reverse, an irf»gular sunken square. See the engravir g No. 1.

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of the chalkos. Gold wae first coined in Greece about the middle of the fifth century B.C.

The workmanship of Greek coins was at first very rnde and barbarous, bnt it gradually improved until, about 500 B.C., it had attained some degree of excellence. But the most beautiful specimens of numismatic art belong to the century extending from 150 to 350 B.C. The coins of Athens are perhaps some of the most famous, and the most remarkable symbol on them is an owl. Pieces of Rhodes have the flowers of the pomegranate, Corinth, a pegasus or winged horse ; Argos, a wolf's head ; Bocotia, a bull's head ; Crete, the minotaur's head, and the labyrinth : Pharsalia, a horse's head ; Marseilles, a lion ; Peloponneaua, a tortoise ; Scio, a sphinx; Sicily, three legs joined; Thessaly, a horse, &c. A hull on Greek coins is supposed to be the symbol of a river.

The most ancient Greek coina are those coined by cities, many of tbem having been struck before tbose of the Macedonian kinga—the earliest princes who coined money. These civic coins generally have on the obverse the head of the genius of the city, or some favourite deity, while the reverse usually bears some symbol used by the city. The inscription contains the initials, monogram, or the complete name of the city. Pinkerton remarks, "Some conoisseurs prefer the regal coins of Greece, others the civic. The former interest by their portraits, the latter by their variety. The former are more important perhaps to ancient history, the latter to ancient geography. To him who is fond of ancient geography, the civic coins, are aingnlarly interesting. It is also pleaBing to see ancient accounts of cities, of their customs, religion, and the like, confirmed by the coins."

The monarchic coins of Greece are usually very iike the civic, except that they generally have the head of the King on the obverse j and a figure of some god or goddess on the reverse, with the name of the prince. Amongst the Macedonian series the coins of Alexander the Great are very fine, and his tetradrachms and drachms are of common occurrence.

The engraving No. 2, represents a tetra

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drachm of Lyaimachus,King of Thrace, bearing on the obverse the head of Alexander the Great as a young Jupiter Ammon. The coins of Alexander himself seldom, if ever, have his portrait.

The later Greek coina struck under the Roman dominion, and having a Roman emperor's bust on the obverae, are ealled Imperial Greek coins.

Ancient coina also exiat of kinga of Sicily, Cyprus, Caria, Ptconia, Heraclia Pontics, Epirus, Egypt (some of thiB country bear the busts of Antony and Cleopatra), Syria, Asia Minor, Sparta, Pergamus, Cassandria, Parthia or the Arsacidai, Persia, Cappadocia, Paphlagonia, Thrace, Poctus and the Bosphorus, the BosphorUB only, Bactria, Ariana, Bithynia, Illyricum, Armenia, Arabia, Mauritania, Galatia, Cilicia, Judasa, Getre, Commagene, Edessa, Palmyra, Gaul, Britain, <fcc.

It may be interesting to give here some account of the Jewish coins mentioned in the Bible. The earliest are shekels and half-shekels in silver, weighing on the average 220 grains troy for the former, nnd 110 for the latter. They are generally believed to have been coined by Si men the Maecabee, on receiving the permission of Antiochus VII., king of Syria about 140 B.C., to coin money with liia own stamp. Seo the Apocrypha, 1 st book of Maccabees, xv. G.

The shekels have obverse, a vase, usually bel;eved to be the pot of mamma; above it is the date in Samaritan characters, "Year 1," "Year 2," or "Year 3." These signify the years of Simon's pontificate, the first one being equivalent to B.C. 113. Circumscription in

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The half-shekclB in silver are exactly similar except that they are rather smaller in size, and have the words "Half Shekel" instead of "Shekel of Israel," ou the obverse.

There are coins dated "Year t," and of very similar design, undoubtedly belonging to the same series as the silver shekels nnd half-shekels.

Copper coins are also assigned to John HyrcanuB, high priest, B.C. 135—106; Aristobulus and Antigonus, B.C. 10U— 1C5 ; Alexander Janneus, high priest and king, Ex. 105—78; Queen Alexandra, B.C. 78—G9 ; .Antigonus, high priest, B.C. 40—37. The common type of the obverse is the name of the prince within a wreath; and of the reverse, two cornucopia united, &c.

The farthings spoken of in the New Testament were the qnadrans and the asttarion, small copper coins worth abcut a farthing. The mite was half one of these.

Coins exiat in brass (or copper) of Herod the Great, and his aucceasors Herod Agrippa I. and Herod Agrippa II. There are also some small copper pieces struck at the time of the revolt of the Jews which ended in the destruction of Jerusalem by Titus, A.d. 70. They have a vine leaf and stalk on one side, and a vase on the other.

The last Jewish coins are silver shekels and

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COLOUR AND COLOUR BLINDNESS By Omicron." (Continued from page \X>\.) rpHE case with which the three primary colour -5- appear to be distinguished by the colourblind, is greatest for yellow and least for red. Yellow, bine, and red is the order in which tbey are most easily distinguished, and we believe no case is reported in which yellow was the colour concerning which the greatest number of mistakes was made. Blue, when well illuminate I, well seen, and some of the colour-blind assert that that is the colour which they can see best, and yet when blue and yellow are mixed,and form green, the number of mistakes is greatly increased, some mistaking it for blue, and the majority for red, and occasionally for yellow. When Dalton first wore the scarlet robes, on his accession totho dignity of D.C.L., he compared it in colour to the leaves of the trees; for him there was no distinction, and in almost every famous case of colonrbliudness the same two colours have been confounded. Troughton, the optician, saw no difference between the peals and leaves of plants. Red is the greatest puzzle to those who confound colours. To sonic, dke Dalton, it has pos;tively no existence, others occisi m.illy see it, but ЯЗ often confound it with green. It is a very curious sight to submit different shades of red ,i:id green wool to colour-blind persons, and :isk them to arrange the wols according to their different colours und shades. Some will lay them out in one sin ■' J'hv, attending with great nicety, apparently,' / rrespective brightness of colour; we say r > , illy, for it is not easy for a normal eye to u "- i!e whether a shade of full green is darker or lighter than a shade of full red. Some will make two distinct bundles, in which the reds and greens will be about equally divided, but possibly the most amusing sight is to see a person debating whether a brilliant red shall be placed nloug with abrightgrcen, and possibly when hehas t/assied right, for he h> s no certainty, he will be unsatisfied with the assortment, and transfer the red to the green bundle. In many cases an artificial light will enable ono who confounds colours to see them as they appear to a normal eye, and if the assorted bundles of red and green wool be laid before them by candle light, their mistakes are in some cases evident to themselves, when ■heir disappointment is sufficiently aggravating. Oreen and red being such stumbling block*, it is not surprising that the more composite colours iu which green and red enter in combination, should prove equally ambiguous to a colour-blind eye. Purple is taken fer blue, the red not being detected ; orange for yellow, olive for brown, and so on. A gentleman communicated to Dr. Wilson the',following account of his own peculiarities of vision:—" As far as I can tell, the following expresas my experience as to colours. Yellow is the far brightest colour, blue nearly as bright ¡ these aro the only two I see distinctly in the rainbow. E;d I can distinguish when bright, but other shades I confound with stone colour or grey. Oreen I have no distinct conception of, according to its different shades it appears black, brown, red, yellow, blue, and groy. I cunuot distinguish at злу distance the ripe cherries on a tree, or strawberries from their leaves. The flowers on the scarlet geranium I cannot see distinctly at a disiince by daylight, but by candle light there is a marked difference between them and the leaves. I have no conception of what is meant by complementary colours, or of the agreement of 'üifferent colours wheu blended together, as, for instance, what kind of a carpet accords with red curtains in a room. With regard to my want of perception of green, it appears to me that the blue and the yellow hues neutralité each other, and would, in equal proportions, constitute what is really no colour, varying from a drab or grey to a dingy black. When the blue rays predominate it appeare blue drab, and when the yellow rays are in excess, it appears a yellow drab. When the blue and yellow are proportionately blended, as in a lady's green silk dress, it appears to be very similar, and no more colour than a drab silk. The dry dirt of the street I should equally suppose to be green. I also confound red and brown frequently. I cannot distinguish between treacle and blood spilt in the street, bv daylight, though I believe I could by candle-light." This peculiarity of vision is best shown by giving the experience of those who have been the sufferers from it, and as these narratives may be the most interasting portion of our paper to tho majority of your readers, we shall make no scruple nor apology for extracting such remarks from other cases as shall best servo our purpose. Dr. K. gives an interesting account of his confusion of colours, but it is too long for completo insertion '* Blue and yellow," says he, " are the brightest oolours. Bed, that is scarlet, is a pleasing sober colour which refreshes my eye as much as green ; indeed, I cannot tell any difference betweencortain shades of these. Ked sealing wax and grass, for instance, are absolutely the same exact colour. Prussian blue and red have the same hue. The rose, the ¡ips, a ruddy complexion, and the face of a man discoloured by nitrate of si ver, are to my eyes absolutaly the same. Bed-hot coals and gamboge yellow are to me identical in colour. Infusion of rod cabbage, deepened by alkalies, or reddened by acids, to me exhibits no change of colour, only a greater intensity or deeper colour j the actual ..olour remains absolutely the same. I cannot detect cherries or strawberries from tho leaves, but by their form. In purchases I have made many mistakes; for instance, I purchased a red ■■dress thinking it a green one. I have on more thau one occasion bought red and green trousers, ihinking they were brown, and had to get them ¡yed afterwards to get them worn. In Paris I 'ought a red cap thinking it a green one; in fact could give many ¡usances of similar mistakes."

When Dr. li. refers to the infusion of red cabbage being darkened by alkalies, he unwillingly furnishes proof as well as 6tatoment of his colour blindness, for the infusion which is originally pnrpb is not deepened in tone, but absolutely changed in tint to a bright green. Dr. Y. says red cibbages growing, pickled, or in infusion, are the most beautiful bines I can imagine, anil it was by not observing any change by acids in the infusion of red cabbage, when attending the chemical class, where I used to stare for the whole honr, expecting to soe the change, that I first became aware of my great defect. The author of these papers had his attention first called to the incapacity, in certain individuals, of detecting colour by noticing that a gentleman to whom he was showing, in a large refracting telescope, the beautiful pair of stars that compose /3 Cygni, saw no difference in colour between the two, and compared them both to the colour of the top part of a gas llame. Any person with a normal eye that has seen these two strongly coloured stars, will own that this gentleman presented a strongly developed case of colour-blindness, aad there cm be little doubt but that a personal equation exists in chromatics as certainly as it does in time, though numerous circumstances render it difficult to arrive at the exact amount of correction that ought to be applied to observers' opinions of colour to reduce them toa uniform standard. The study of sidereal chromatics requires a very correct eye for colour, and the correct determination of colour of stars affords a most convincing proof of the entire absence of anything approaching to the phenomenon that we have attempted to describe in this paper; to those who are interested in this particular study, we recommend Admiral Smyth's work on " Sidereal Chromatics."

As in all tho cases we have mentioned the symptoms of colour-blindness displayed themselves at a very early age iu each subject,-it is not absurd to suppose that the defect was congenital, but there is one notice ou record where colour-blindness was the result of iojnries received from an accident, and this circumstance is of the highest importance, as it points out the probability of pathological inquiry revealing the true cause of colour-blindness, and eventually teaching to scientific men its successful remedy. This gentleman, a surgeon himself, had been thrown from his horse, and snstainod a concussion of the brain, and there can be little doubt but that to this circumstance is to be traced the insensibility to colour that the eye of this gentleman ever after retained.

It will not have escaped the attention of the careful reader that in every case mentioned but one, the subject of colour-blindness has been a male, lie will naturally be led to inquire whether the defect does not make its appearance in females. That there are cases of colour-blindness to be met with iu the "softersex" is undoubtedly the fact, but the instances are much rarer, and when they do occur, the ingenuity of the unhappv subject is exerted to its fullest extent to keep the defect from being noticed. Dr. Wilson, in carefully prosecuted inquiries for a term of nine months, discovered only six cases, and had the opportunity of examining but one. The unwillingness that ladies have to confess their inability to detect shades of o»lonrs makes the rarity appear greater than is really tho case, as we before hinted, and Dr. Wilson notices that women of the better class, who had to make purchases where the defect might be noticed, usually brought a friend with them to avoid detection. In arriving at any accurate statistics with reference to women, a great difficulty is felt in meeting with large bodies of women together, who can be submitted to a trial. This defect is supplied with men by examining a section of the army or police force, or any other body of men, but except in the case of factory girls (whose want of education renders them peculiarly unfitted for a trial of this description), or lunatics, who are also not desirable for evident reasons, it will not be easy to meet with a large collection of ladies on whom to experiment. Dr. Wilson's inquiries were ш-ide in the shops of haberdashers and silk mercers, and the result of hLs inquiries can hardly be regarded as satisfactorily settling the question of the proportion of the mule to the female colour-blind.

Dalton was the first to attempt to inquire what proportion of the population were colour-blind, but his inquiries were not sufficiently extended to lead to any accurate results. lie remarks—" That out of 25 pupils that I once had, to whom I explained this subject, two were found toa^ree with me, and ou ai.oàici- similar occasion oue." Pro

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fessor Subeck¡found fiveoiit of -1 > i voutbs, who composed the two upper classes in a ^yumasium at I3erlin, to be colour-blind. Professor Pierre Pr?vos,t dci'aredthattliecolour-bliul amount tolii)20, ami Professor Wartmann did not think that the last estimate was a great exaggeration, for hesav^, "I have readily found i nnmlw of persons affected with this singular nnomuly."* Tho carefully-conducted, and much more widely-extended examination of Dr. Wilson is the most reliable with which we are acquainted. The total number examined was 1151t, principally soldiers and members of the police force. Of these 1151, 21 confounded red with green; 19, brown with green; 25, blue with greeu. The total number to some extent colour-blind was therefore 05, or 5'C per cent., which gives 1 in every 177 persons as marked with this extraordinary anomalous vision. "For my own part I think it probable that the number of persons in this country ns markedly colour-blind as Dalton was—i.e., givel to mistake red for green, brown for green, for blue, and occasionally even red for bf not loss than 1 in 30; and including all kinds aft! various degrees of colour-blindness, 1 in 'M."X We are not able to offer any statistics having reference to observations as to colour-blindness made in any other part of the world, but it seems not unreasonable to suppose that in a country wherenumbers are obliged to follow occupations which do not give full exercise to the external senses, the kceaness of perception may not be so great as in countries where the senses are more eagerly trained. The susceptibility of the inhabitants of the higher latitudes to colours is far inferior to that of the race who produce the magic dyes of India, or the still nobler one that built the glowing wall» of tho Alhambra. Even our neighbours the FreDch excel us in this matter, and it is not perhaps saying too much to assert that most of the civilised, and even the barbarian people, excel us iu a taste for colours.

Before we conclude these few remarks on Daltonism, or colour-blindness, or whatever name the reader may give this peculiarity, ib is desirable that we mention a few of the causes that have been assigned by medical and scientific meu to account for tbe defect, and, perhaps, first ot all.wffl arise the question whether the peculiarity is to he traced to the physical formation of the eye, and whether the simple inspection of the organ could decide whether a person was a sufferer from colonr-blindnes3 or not. And here possibly opinions will differ according to the sentiments of tho readers, and if he be a phrenologist he may decide that a knowledge of that science (some perhaps will object to the term science) is sufficient to recognise an abnormal eye. One of the accounts that we have partly quoted, and whose length did not permit of the entire recital, adds tho following testimony in favour of phrenology: "The only fact which somewhat staggered mo relative to phrenology was that a phrenologist, then unknown to me, now a valued friend, asked me one day to answer him candidly whether I knew colour, as in mo tho bump of colour was absent. Several phreuologists who have seen my head since have agreed as to the absence of the so-called bump." The only case iu which a colourblind eye has been submitted to a post-mortem examination (so far as we are aware, with tho exception of some general observations by Mr. White Cooper), was thtt of Dalton, at which Mr. Bally, formerly assistant to Dr. Spurzheiin, was present, and took casts of several parts of the brain and skull. "Ho (Mr. Bally) pointed out a remarkable prominence on the frontal portion of the orbitar plates (which represents the phrenological site of the organ of colour, and the imperfect or deficient development of tho convolution of the anterior lobes, which rested upon them. Of course Mr. Bally adopted this as the true explanation of the peculiarity of Dalton's vision; and we as witnesses not only without faith in phrenology, but even opponents, are bound to record the fact." But although wo have arranged these two cases side by side, as boing prominently marked out by phrenologists, as establishing their theory, there is in reality no connection between them, for those who have seen Dalton's bust, by Chantrey, will see that the superciliary ridgo is projected very markedly, so as to overhang the eyes, a»d would have been selected by pkrenulogists as a sign of the possession of an exquisite sense of colour.

(To be concluded ni-xt werlc.)

* "Taylor's Scioutític~Xíem ilr«7*TrtM~ + Thi-* number includes lôO of l'roíessor KcUaod'i pupils,examined by llinc irontleiuan. % Dr. (i. Wilson, Op. Cit.

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1CIENCE FOR THE YuUNG.

.EV. E. KEnXAJÎ,CLOXOOV.-ES COLLEGE. (Confiiiiitd from paje 154.) § IV.—Attraction*. exist varions sorts of attraction, which divided into two classes—I. Attraction JE at a distance; II. Attraction sensible fence. The first class contains attrnotion /position, or chemical attraction: attracf cohesion, the force by which the particles body hold together, or, as it is commonly "d, "molecular attraction;" attraction of ado, the force whieb, nnitcs separate bodies of ame or different natures. The second class ^prises electrical and magnetic attraction, and f attraction : attraction of gravitation. Chemi1, electrical, and magnetic attraction are studied their own treatises; 'mechanics" deals with ttraetion of cohesion, adhesion, and gravitaion.

No. I.—Laws.—Tho three sorts of attraction are included in one set of Laws.

Law I. Cohesion exists in all bodies. Solids, liquids, and eren gases, have a force by which taeir particles are held together. That which is e'early seen in the solid state exists in the other state, though very much diminished.

Law II. Cohesion Taries in different bodies, and in the different states of the same bodies. It is more in some solids than in others, and diminishes as the solid passes to the liquid and gaseous state.

Law III. Adhesion may be observed between bodies in all states. Solids adhere to solids, to liquids, to gases; liquids to liquids and gases; even perhaps gases to gises.

Law IV. All bodies attract one another. It may not be perceived by an effect of motion, but the effort at motion exists, between the greatest and smallest.

Law V. Attraction of gravitation is inversely as the square of the distance. In formnla G D's

(G gravitation, D distance); — = \ В jo

G- Dj" This fractional form of proportion will always be used, and will be found, after a little custom, to be very convenient. 2. The letters with a dash (G' D') will always signify the subject matter in other conditions. Thus here G' D' signify either the gravitation of a second body at its own distance, or that of the same body, at a now distance. The full expression contained in the formula is, the gravity of one body is to the gravity of another as the square of the distance "of the second is to the square of the distanceof the first; or, the gravitation of a body in one position, is to' the gravitation in a se;ond"position, as the square of the distance oí the second position is to tho square of thedietance of the first. And this be it said once for all, is the method of formulis'ing "inverse proportion." Law VI. Gravitation is directly proportional

. >v G Л1

to the mass of matter. In formnla — = — the

. . G' M'

gravity of one body is to the gravity of another as the mass of matter of the first is to the mass of matter of the second.

No. IL—Proofs.—Almost all these laws admit of experimental proof. Some proofs, however »re not what are called class experiments.

Law I. That solids have their particles cohering requires no ргооГ. Liquids: A rod of glass dipped into melted glue, water, or spirit lilt« from each a drop, smaller as the perfect liquid state is approached. These drops consist of particles held together bv cohesion. In gases there is inch a predominance of an opposite force tnat it is not easy to prove the existence of cohesion ; yet analogy to tho other states seems to require it, 0f course in a verv diminished condition; and the cnfc with which the heavy visible gases can be drawn about, so to speak, almost proves what analogy suggests.

Law II. The great difference of force required to separate the particles of different bodies The 'trongest man cannot pull asunder a small oTlinoeroi iron ; the weakest boy can pull asunder a 4 linder of eld.-r pith. Lead in the solid state is ►trong m cohesion; in the liquid it is not much more than water. Watet in the solid state

XJ? ¡и*" ^eth.er .weU; ae MMm -- hus bnt

ins qnestionable cohesion of a gas.

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bullets, a part of each being removed, when well pressed together, will bear a considerable weight even as much as 201b. weight. This experiment was first shown by Triewold. Wax may be used but it is not so convincing. Between solids and liquids. The glass rod lifts the liquid (Law I) by means of their mutual adhesion. But there is an experiment, said to be Taylor's, and celebrated for the controversy to which it gave rise which affords a very convincing proof. To one of the pans of a balance is hung a flat disc. By weight in the opposite pan, equilibrium is restored 1 ress the disc down gently to a tray of water underneath: remove the hand, the disc, and with it the balance arm is held down by the adhesion of the water and the disc, Fig. 10. A considerable increase of weight m the opposite pan is required to raise the disc. The increase of weight varies with the liquid; it is less as the fluidity is more perfect. When the disc is forced gent'y up the cohesion of the liquid state is well seen "The water is drawn up in a hollowed form, Fig. 20, growing thin cer as the

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withdraw some of the liquids arc usually held

disc rises. Between solid and gases. Into a deep receiver of glass, Fig. 21, is passed down by means of a wire a leaden capsule filled with largo shells of granulated zinc. Set the receiver aside in a q uiet room for a day or во. The zinc decomposes the water slowly (a little acid might be added to quicken the action). After some time the shells of zinc will be seen covered with shining bubbles of gas, which, though under considerable water pressure, forcing them up, still adhere to the solid. A slight shock to the capsule — raise it a little and strike it against the bottomproduces a been itul "shower" up of silverlike bubbles, Fig. 22. Left quiet again for an hour or two, bubbles of gas will be again found on the zinc. Between liquids and liquids. A tube of glass wet with water, dipped into oil, will oil, although these to be repnlsive one of

gasean to a great extent be liberated without any change of pressure. For instance—by stirring soda water, champagne, &0., with a bit of bread, the gas will be freed. As to gases, and gases perhaps, the law of "perfect mixture" may be caused by adhesion. However, the nature of the gaseous state does not seem to require that help to the action of Bertliollot's law. Law IV, being Newton's great discovery, and serving in his hands to explain all the difficulties and remove all the absnrd and contradictory notions regarding tho system of the nniverse, ought to be more than sufficient to establish it» truth. However, this is not all. It has been proved in two ways. The first was an accidental result—tho second by means of an apparatus constructed in part specially for the purpose, ihe accidental discovery was made in Pera where some French philosophers wero carrying ont a series of astronomical observations at either side of Chimborazo.

They found, on comparing results, that their instruments pointed differently at their respective sides of tho monntain. The "pointing'' of the instruments was controlled by a line with a small weight hung to it. Since, then, the instrument* pointed differently, the position of the line must be different. The cause assigned was that tho moantain attracted the weight, and consequents pave a different pointing. The astronomical observation required was the "zenith distance' ot a star—г е., tho distance of a star from a point vertical to the observer; Fig. 23 (S) a trvr

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the other. Between Uquuli migases. The

zenith distance. The instruments guided bv incline and weight made it S h at one side, and S , at the other. Tbii remarkable fac: having causei}

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WHAT STRIPES THE SUNBEAM. By л Fellow Of Tue Royal Astronomical Sot I Sty. (Continued from page 14G.) "VJ 0\V, remarkable as all this is, it is in its lead-Á-i ing features by no means new. Nearly 120 yens ayo Melville observed the yellow tint communicated to flame by soda, and Sir David Brewster revived this idea in 1822 in his invention of the monochromatic lamp. Nay, Sir John llerschel, in the same year, instituted experiments on the spectra of varions substances, and notably of strontium and of the chlorides of copper; and in his •' Treatise on Light," in the " Encyclopedia Metropolitana," Vol. 4, published in 1827, says :— "The colours thus communicated by the different b'jse.s to liame, afford in many cases a ready and neat way oí detecting extremely minute quantities of them.'' Among the names if those who pursued this curious train of investigation, we find, too, the honoured one of Fox Talbot— perhaps better known as the practical originator of photography in England, and the inventor of the Talbotype; and he, albeit erring in his determination of the elements to which certain lines were referable (and notably with regard to the yellow line of sodium, of which we have previously spoken, and which he attributed to water !), yet points out clearly how the spectra of particular elements supply unerring means of deciding what those elements are. Next, as we »pproach our own time, we find Professor W. A. Miller, F.R.S. (whom we shall by-aml-bye have to speak of as the associate of that eminent astronomical sprectroscopist, Mr. William Huggius, F.R.S., iti his researches on the chemical constitution of the heavenly bodies) pursuing investigations into the spectra of the metals of the alkaline earths. Then, in 1837, Swan showed conclusively how the single yellow line which we have mentioned above was produced by sodium; and how, moreover, this element was everywhere present in earth, air, and sea; so tunt, light our lamp where we may, it is almost with a moral certainty that the combustion of sodium will at once commence.

It is, however, to two German philosophers, BLiusen and Kirchhoff, that we may be said to owe spectrum analysis in the form in which we now possess that most potent addition to chemical science. Commencing their experiments on the spectra of tliu metals, some year or two alter the period at which Professor Swan was at woik on tho subject, they, in their laboratory at Heidelberg, gradually built up, on a .solid foundation, that marvellous theory by the aid of which we are able to look out into the dim confines of space, and assert that certain elements are present in, or absent from, the infinitely distant bodies which tenant it. Let us try and follow their reasoning, and see how they arrived at i-o very wonderful a conclusion ; albeit to do this wiil involve some slight repetition of what we have previously said. Ae our aim is, however, al'ore all things, to secure clearness «lid perspicuity in our explanatiou, a little reiterat.ou is unavoidable.

They began, then, by volatilisingorvnponrising the substances whose spectra they wished to examine by means of what is known as a "Bii'iBen's gas-lump," or " Biinsen's burner," the invent on of one of the experimenters himself. One form of this is represented in Fig. 4. The gas passes through the supply pipe *, into a perforated chamber c, where air mixes with it ; they both rush up the lube с t, in combination, anil the mixture is ignited at (; r represents a ring burner to mike a larger circle of flame. This li-e in at Л The effect of this arrangement is to cons uno the solid carbon particles in the coal gas

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with great rapidity, and, consequently, to give a flame which, while tremendously hot, emits scarcely any light at all. The great advantage of this arrangement will be evident when we reflect that in dissolving varions substances in alcohol (or spirits of wine) and burning that, when we examino the resulting flame with our prism, we not only get the spectrum of the dissolved substance, hut that of the burning alcohol as well, thus complicating the observed appearance in a very perplexing way. On the other hand, with the fiercely hot, but scarcely luminous flame of the Bünsen burner, we get practically nothing but the incandescent vapour of the particular eubstance which we may have under examination. Employing, then, this simple and ingenious apparatus, in conjunction with their spectroscope, Kirohhoff and Bünsen soon convinced themselves that " the most different salts of the same metal, if they are volatile, produce the i-ame bright lines in the spectrum, but with different degrees of brilliancy : and that a mixture of salts of different metals gives я. spectrum similar to that which would be produced by a superposition of the several spectra of the individual mit ils." In his original memoir, Kirchhoff, after speaking of the recognition of the linesof the several metals under varying circumstances of their production, goes on to say—and this is of the veiy greatest possible importance—"The dark lines of the solar spectrum afford invaluable assistance in determining the position of the bright lines of the elementary bodies." He then proceeds to describe an arrangement entirely similar in principle to that illustrated in Figs. 2 and 3, and observes—"In this way, whilst in tho upper half of the field of the (astronomical) telescope, the solar spectrum is seen, in the lower half, but in immediate contact with the other, the spectrum of the artificial source of light becomes apparent, and tho positions of the bright lines in the latter spectrum can be accurately compared with those of the dark lines in the solar spectrum. In ord»r to obtain the spectra of the metals, I have almost invariably employed the electric spark, chiefly owing to its great luminous intensity." To this we may add that the spectrum of any body gaseous under ordinary condition, such as carbonic acid, hydrogen or nitrogen, is obtained by the passage of the electric spark through the gas under examination, which is itself sealed up in a glass tube ; and that cvon to the naked eye, the difference «f colour presented by the spark is most noticeable, it appearing blue iu carbonic acid, red in hydrogen, and yellow in nitrogen. And here, although we arcslightly anticipating, wecanuot forbear to notice that when we examine the spectrum of this red hydrogen epark we find it to consist of merely three bright lines—one red one so brilliant as almost to overpower the others ; one bright greenish-blue one, anil one dark blue, or almost indigo line, which is naturally not so bright ; and that the fact of the most vital importance in connection with this is that these three lines are found to be abtolutcly coincident with three of the well-known darle li/ws in the Sun's light, of which we spoke on p. 146, as "Fraunhofers lines," when compared with them in the way indicated above.

And now, in order that we may comprehend and realise the import of the great discovery of Bünsen and Kirchhoff, let us, as it were, take stock of the knowledge which we are so far in possession of. And, firstly, we have learned that overy incandescent solid or liquid, when its light is examined by means of a prism, gives off a continuous spectrum—that is to say (assumi»ii: its temperature to be sufficiently high) one,

which, starting from the least rerrangible en I, consists of red, orange, yellow, green, blue, indigo, and violet rays, successively melting into each other without break er interruption of any sort or description. Then we have seen that if we examine the light of an incandescent gas or vapour, we no longer find it yielding a continuous spectrum, but one of rays of relatively few degrees of refrangibility ; Go that in regarding a narrow slit illuminated by such li^ht, through a prism, we obtain a spectrum consisting of bright lines in various parts of the solar spec trum, but separated by intervals of to'al darknes>. Listly, we have tho discovery of Woll iston, or perhaps rather of Fraunhofer, that the Solar Spectrum is crossed by a series of stripes, lines, or shadows, whose places in it are fixed nnd invariable; that these lines are seen in all light derived directly or indirectly from the Sun, such as that of the day sky, the moon, the planets, &c, and that although some of the dark lines pertaining to sunlight are found in certain of tho fixed stars, yet that others are absent We stated on p. 116" that Fraunhofer liad mapped between ô and COO of these lines. We may here add that more recently Kirchhoff and Angstrom have increased the number to very many hundreds, some of them being of the very last degree oí faintness.

In figures 3 6 and 7 we have endeavonred to give some faint pictorial idea of what we have been describing; but it is obviously impossible to reproduce in black and white upon a wood block the chromatic phenomena exhibited. Fig. 5 is intended for the Solar Spectrum: Fig G for that of Sodium; and Fig. 7 for that of Hydrogen. Well, then, in 1814, Fraunhofer discovered that when he got the spectrum of the Sun (Fig. 5), and the spectrum of Sodium (Fig. 6), into tho field of his telescope ¡¡together, the dark line which he lettered D, and the yellow line of sodium, were coincident, each appearing as the mere prolongation of the other; and in 1S49, the great French physicist Foucault, noticed, on passing direct solar light through the vapour of sodium that the dark line I) came out in the spectrum of the Suu with startling distinctness. There facts, however, remained barren until ¡So'.), when Kirchhoff and Bünsen began their investigations, which eventually led to such surprising results, and the exceeding imponance of Kirchhoffs crucial experiment is such that we will give his account of it in his own words : " In order," he says, " to test in the most direct manner possible the truth of the frequently asserted fac: of the coincidence of the sodium lines with ike lineo D, I obtained a tolerably bright solar spectrum, and broughta flame coloured by sodium vapour in front of the slit. I then saw the daik lines D change into bright ones. The flame of a Biinseo's lamp threw the bright sodium lines upon the solar spectrum with unexpected brilliancy. In order to find out the extent to which the intensity of the solar spectrum could he increased, without impairing the distinctness of the sodium lines, I allowed the full suuli-ht to shine through the sodium flame upon the slit, and, tu my astonishment, I saw that the dark linea 1) appeared with an extraordinary dearea "f clearness. I then exchanged the sunlight fur the Drummoud's or oxyhydrogen linie-lighr, which, like that of all incandescent solid or liquid bodies, gives a spectrum containing no» lark lines. When this light was allowed to fall hrough a suitable flame coloured by common salt, dark lines were seen in the spectrum in the position of the sodium lines. Tho same pheno:iien.n was observed if instead of the iucande- J

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